E30 Zone

Hi,
i`m a newb,
i`ve got a problem with my rear brakes
if i brake hard (*hard*) then the rears lock up, it`s mot time soon so i really need to fix this now has anybody any idea where to start
the brakes pull up quite well and the black marks of runbber on the road are of a similar length so i guess both of the back brakes are the same.
Could that mean the compensator has failed?
Also when going over rough road surfaces at about 25 - 30 mph the front suspension seems to jiggle over the bumps, not up and down more like from side to side it seems to me that something is worn but again where do i start?
please help
......oh it`s a beautiful alpine white 4 door (like that matters)
318i with 140,000 miles on the clock

I'd guess front ball-joints and/or bushes may well be shot, and most likely front pads and discs.